The use of inkjet printing in offices and homes has grown dramatically in recent years. The growth can be attributed to drastic reductions in cost of inkjet printers and substantial improvements in print resolution and overall print quality. While the print quality has improved drastically, research and development efforts continue toward further improving the print quality to achieve images having photographic quality. A photographic quality image includes saturated colors, high gloss and gloss uniformity, freedom from grain and coalescence, and a high degree of permanence. To achieve photographic image quality, the print medium must be fast drying and resist smearing, air, light, and moisture. In addition, the print medium should provide good color fidelity and high image resolution.
In order to obtain printed images that dry quickly and have good image quality, durability, and permanence, microporous inkjet print media with thermally laminated barrier layers have been developed. While lamination of the printed image provides very good image quality and permanence, the cost of producing the laminated images is increased due to the cost of the laminator and the additional supplies that are necessary. In addition, lamination produces haze and air bubbles, which become trapped, decreasing the image quality of the printed images.
Print media that are capable of producing images having photographic image quality are typically categorized into two groups: porous media and swellable media. Porous media generally have an ink-receiving layer that is formed from porous, inorganic particles bound with a polymer binder. An inkjet ink is absorbed into the pores of the inorganic particles and the colorant is fixed by mordants incorporated in the ink-receiving layer or by the surface of the inorganic particles. Porous media have a short dry time and good resistance to smearing because the inkjet ink is easily absorbed into the pores of the ink-receiving layer. However, porous media do not exhibit good resistance to fade. In swellable media, the ink-receiving layer is a continuous layer of a swellable, polymer matrix. When the inkjet ink is applied, the inkjet ink is absorbed by swelling of the polymer matrix and the colorant is immobilized inside the continuous layer. Since the colorant is protected from the outside environment, swellable media have greater resistance to light and dark/air fade than the porous media. However, the swellable media generally have reduced smearfastness and a longer drytime than porous media.
To overcome the problems with porous and swellable media, fusible or sealable print media have been developed and continue to be researched. After a desired image is printed, the fusible print medium is exposed to heat and/or pressure to seal a fusible layer over the printed image. The sealed, fusible layer forms a protective film over the printed image, helping to protect the printed image from scratches or fading. While this printed image has a greater resistance to light and dark/air fade, the image is typically non-glossy and has a low gamut. The fusible layer is typically formed from a polymeric material that has a high glass transition temperature (“Tg”), such as a high Tg latex. The polymeric material prevents the polymer from coalescing at ambient temperature and improves scratch resistance of the printed image. However, a large amount of energy is used to fuse the fusible layer. The amount of energy or heat required to fuse the fusible layer is referred to herein as a fusing energy. The fusible layer typically requires that a temperature of greater than approximately 90° C. is reached and maintained for 30 seconds or more to fuse the fusible layer. Since a long dwell time at an elevated temperature is required, printing throughput on the fusible print medium is low and is limited by the print speed of the inkjet printer. As such, the fusible print medium is used with a slow inkjet printer or a slow inkjet print mode. Therefore, fusible print media typically have a low fusing efficiency. As used herein, the term “fusing efficiency” refers to an amount of time that is used to fuse the fusible layer of the fusible print medium. If less time is needed to fuse the fusible layer, throughput is increased.
To improve the fusing efficiency of fusible print medium, low Tg polymers have been incorporated into the fusible layer. However, the low Tg polymers are problematic because the fusible print medium may be prematurely fused, which damages print quality and image quality. The surface of the fusible print medium is also more prone to scratch damage. Infrared absorbers have also been included in the fusible layer to improve the fusing efficiency. However, the infrared absorbers require radiative heat to become activated and, therefore, are not practical for home use. In addition, the infrared absorbers are expensive, are soluble in solvents, and impart a color to the fusible layer. Liquid plasticizers have also been added to inkjet inks to improve the fusing efficiency of fusible print medium. Since the liquid plasticizer is a component of the inkjet ink, it passes through the fusible layer with the inkjet ink. Therefore, the liquid plasticizer does not remain in contact with the fusible layer for a sufficient amount of time to aid the fusing of the fusible print medium.